My new PR511's motion detector on the garage that illuminates my driveway was cycling on and off every couple of minutes.
I traced the trouble to a light fixture mounted 10 feet away that was throwing some light on my driveway, a nearby tree, and on the PR511 motion detector.
I installed a shield in the light fixture that now keeps my driveway, the tree, and the PR511 motion detector in the dark.
With the sensor now in relative darkness, the PR511 is only triggered by motion, and I am not seeing any false on-off cycles in the ActiveHome Pro Activity Monitor.
I do not know if it was keeping light off the tree, whose branches were moving in the breeze, or the motion detector, or both that helped, but now there have been zero false alarms all night.
Thinking it was only heat changes that would trigger the motion detector, I did not realize until now how ambient light can cause the PR511 motion detector to not operate correctly.